No problem, let's work through this together. We're starting with 603 and 4005 and adding them all up.

Step 1: We'll start by adding the digits 3 & 5 in column 1 and get 8.

Step 2: We'll start by adding the digits 0 & 0 in column 2 and get 0.

Step 3: We'll start by adding the digits 6 & 0 in column 3 and get 6.

Step 4: We'll start by adding the digits 0 & 4 in column 4 and get 4.

So, 603 + 4005 = 4608.

